The present invention relates to an insulation resistance tester having a meter with a logarithmic scale for indicating resistance values.
Various circuits have been used for logarithmic conversion in the insulation resistance tester, such as a circuit using the Zener characteristic of Zener diodes, a circuit using an approximating polygonal line provided by diodes, and so forth. The first-mentioned circuit, however, requires specially selected Zener diodes, while the second-mentioned circuit requires a large number of parts.